ELECTRICAL-IMPEDANCE TOMOGRAPHY USING INDUCED CURRENTS

The mathematical basis of a new imaging modality, Induced Current Elec trical Impedance Tomography (EIT), is investigated. The ultimate aim o f this technique is the reconstruction of conductivity distribution of the human body, from voltage measurements made between electrodes pla ced on the surface, when currents are induced inside the body by appli ed time varying magnetic fields. In this study the two-dimensional pro blem is analyzed. A specific 9-coil system for generating nine differe nt exciting magnetic fields (50 kHz) and 16 measurement electrodes aro und the object are assumed. The partial differential equation for the scalar potential function in the conductive medium is derived and Fini te Element Method (FEM) is used for its solution. Sensitivity matrix, which relates the perturbation in measurements to the conductivity per turbations, is calculated. Singular Value Decomposition of the sensiti vity matrix shows that there are 135 independent measurements. It is f ound that measurements are less sensitive to changes in conductivity o f the object's interior. While in this respect induced current EIT is slightly inferior to the technique of injected current EIT (using Shef field protocol), its sensitivity matrix is better conditioned. The ima ges obtained are found to be comparable to injected current EIT images in resolution. Design of a coil system for which parameters such as s ensitivity to inner regions and condition number of the sensitivity ma trix are optimum, remains to be made.